1. Field of the Invention
The invention relates to a light-emitting device, and more particularly to a light-emitting device with a uniform light-mixing effect.
2. Description of the Related Art
Some light-emitting devices can output white light by mixing light from red-light, green-light, and blue-light light-emitting diode (LED) chips.
Referring to FIG. 1, a conventional light-emitting device 1 includes a package housing 10, a red-light LED chip 21, a green-light LED chip 22, a blue-light LED chip 23, and a transparent package filler 30.
The package housing 10 may be composed of white plastic or ceramic material.
The red-light LED chip 21, green-light LED chip 22, and blue-light LED chip 23 are disposed in the package housing 10 and separated from one another. Moreover, the red-light LED chip 21, green-light LED chip 22, and blue-light LED chip 23 may be arranged in a triangular form as shown by FIG. 2A or a linear form as shown by FIG. 2B.
The transparent package filler 30 may comprise silicone sealant. The transparent package filler 30 is filled in the package housing 10 and covers the red-light LED chip 21, green-light LED chip 22, and blue-light LED chip 23.
When the red-light LED chip 21, green-light LED chip 22, and blue-light LED chip 23 simultaneously irradiate, light output therefrom does not possess directionality and is scattered by an inner wall of the package housing 10, thus forming asymmetric irradiation areas, and further causing a non-uniform light mixing effect. For example, as shown in FIG. 2A or FIG. 2B, the red-light LED chip 21 contributes to a red irradiation area R near the center of the package housing 10, the green-light LED chip 22 contributes to a green irradiation area G near the right of the package housing 10, and the blue-light LED chip 23 contributes to a blue irradiation area B near the left of the package housing 10. Because the light output from the red-light LED chip 21, green-light LED chip 22, and blue-light LED chip 23 is scattered by the inner wall of the package housing 10 and the distribution of light intensity in the red irradiation area R, green irradiation area G, and blue irradiation area B is not uniform, a mixed white-light area W (depicted by diagonal lines) formed by overlapping the red irradiation area R, green irradiation area G, and blue irradiation area B is small and the light color thereof is not uniform. Moreover, other mixed colored-light areas are formed around the mixed white-light area W by overlapping of every two of the red irradiation area R, green irradiation area G, and blue irradiation area B. Accordingly, as the effective mixed white-light area provided by light-emitting device 1 is small and a white-light mixing effect provided thereby is poor, the efficiency of optical application of the light-emitting device 1 is low. Namely, utility of light color of the light-emitting device 1 is low.